Presently, disposable materials made of non-woven fabrics for medical use such as surgical caps, surgical sheets, surgical covering clothes, surgical gowns are spreading rapidly. Problems of hospital infection such as an infection of MRSA (methicillin-resistant Staphylococcus aureus), hepatitis, HIV (human immunodeficiency virus) or O-157 necessitate the use of disposable materials. Further, using disposable non-woven materials requires no necessity for cleaning, so that nursing can be simplified without deteriorating nursing quality. Also it can be one of solutions for a labor shortage that has been becoming serious social problem. The non-woven fabric for medical use is required to have bacteria barrier property, anti-permeability, water repellency, lint free property and so on, but also importantly the fabric is required to have good wear feeling, strong tenacity and cost performance because the fabric is disposable for only one time use.
As raw materials of fibers for a non-woven fabric, polyethylenes, polypropylenes and polyesters are widely used. It is conventional to use these raw materials to make non-woven fabrics for medical use. However, the fabrics made with these raw materials have some disadvantages. For example, non-woven fabrics for medical use are frequently disinfected under radiation. Polypropylene fibers lose their tenacity under radiation because chemical bonds on tertiary carbon atoms are cut, thus making polypropylene not very suitable for as a non-woven fabric material. While radiation does not weaken the tenacity of the polyester fibers, the cost of polyester resins is higher than polyolefin resins. And when polyester non-woven fabric having high basis weight is used to make the fabric tenacious enough to avoid being torn by user's body action, or to make the fabric opaque, the fabric becomes hard and has poor wear feeling, or lacks a light feeling due to the nature of the polyester resin. Because of these disadvantages, polyester non-woven fabrics are not generally used to make fabrics for medical use. Contrary to this, polyethylene resins are useful in making non-woven fabrics for medical because they produce soft non-woven fabrics due to the nature of the resin material. In addition, polyethylene resins do not have tertiary carbon atoms to weaken the tenacity under radiation.
However, conventional polyethylene fibers do not have enough stiffness due to the raw material resin's nature of softness, so it has been a problem that crimps which withstand a tension under carding process cannot be provided. It has been conventionally known that some polyethylene fibers and non-woven fabrics experimentally obtained are very soft, but in view of commercial practice, it has been very difficult to process them into high quality non-woven fabric at low cost, so a polyethylene fiber having good cardability is strongly desired. As a polyethylene fiber for medical use, for example, Japanese Tokkyo Kohyo Koho Hei 6-508892 (corresponds to PCT gazette WO93/01334) discloses a composite fiber composed of a high density polyethylene as a core component and a copolymer of ethylene and other .alpha.-olefin (described linear low density polyethylene hereinafter) as a sheath component. However, the above fiber has weak retainability of crimps due to low breaking tensile strength and high breaking elongation, so that when the fiber is wound on a cylinder or doffer during the carding process, it may not be well ejected as a web or sometimes it makes neps. Thus, there some problems associated with conventional polyethylene fibers employed in the prior art.